1. Field of the Invention
The present invention relates to a safety function with respect to an optical fiber used in a projection display apparatus in which a laser beam source and the optical fiber are included.
2. Description of the Related Art
In a conventional projection display apparatus, an incoherent and relatively low brightness light source such as a mercury lamp or a light emitting diode (LED) has been used. An example of a thin optical system whose light source is a mercury lamp is disclosed in page 6, and FIG. 2 of Japanese Patent Application Publication Laid-Open No. 2006-91867 (Patent Document 1). On the other hand, because a laser system excels in its beam directivity and high brightness, the system is useful as a light source used in a projection display apparatus. By installing a laser beam source, a compact optical system can be obtained, and a compact optical engine suitable for thinning a projection display apparatus can be obtained (as to an example of a projection display apparatus that utilizes a laser beam as its light source, refer to page 4 and FIG. 1 of Japanese Patent Application Publication Laid-Open No. 2000-131665 (Patent Document 2)).
By using a laser beam excellent in focusibility as a light source for a projection display apparatus, the optical engine thereof can be made compact. However, because in the system the laser beam source and the optical engine need to be arranged collinearly with each other, the degree of freedom of arranging parts of the system in the projection display apparatus is relatively low; thus, thinning of a overall projection display apparatus has been restricted. In order to solve the problem, if the laser beam source and the optical engine are connected to each other through an optical fiber, because light can be transmitted through the optical fiber even though it is bended, the laser beam source and the optical engine connected through the optical fiber do not need to be arranged collinearly with each other; therefore, the degree of positional freedom of placing the parts is increased. Thinning of the overall projection display apparatus can be resultantly realized.
However, when a laser beam is transmitted through an optical fiber, because the optical fiber may be damaged due to local heating up, a system safety needs to be secured against temperature rise.